The present invention relates to an optical multiplexing module wherein the optical axis can be aligned between at least two collimators, each fixed to a cylindrical member, arranged at the input and output ends of the module, and a method for aligning the optical axis thereof.
There has been known an optical multiplexing module that has at least two collimators and a cylindrical member wherein the collimators are fixed with their optical axes aligned to each other. FIG. 7 exemplifies the structure of such an optical multiplexing module 100, wherein a section of the module is outlined. The module 100 has two collimators 102 and 104 secured to the input-side end thereof and one collimator 110 at the output-side end thereof. Optical rays that enter the collimators 102 and 104 are multiplexed into the collimator 110 with the help of a prism 106 and an optical connector 108.
In manufacturing such module 100, it is required that optical axes be aligned (also known as xe2x80x9calignment adjustingxe2x80x9d) so that an optical loss between both of the optical-input collimators 102 and 104 and the optical-output collimator 110 are minimized. The collimator(s) is fixed in position in the cylindrical member 112 at one side thereof, and then the collimator(s) is adjusted to an optimum alignment position that minimizes optical losses.
Joint portion(s) between the collimators 102 and 104 or collimator 110 and the cylindrical member 112 are then fixedly connected with laser welding such as a YAG laser. The collimators 102, 104, and 110 are inserted into cylindrical cavities 118, 120, and 122 drilled in the cylindrical member 112, respectively, and secured there. An outer surface of each of the collimators 102, 104 and 110 makes a circular line contact with an inner circumferential edge of each of the cylindrical cavities 118, 120 and 122, thus forming the joint portions. That is, each joint portion is circular in its contacted shape. Laser beams are irradiated onto each circular joint portion at twelve to fifteen points in such a manner that all the positions are equally spaced to each other.
The radiation is carried out, for example, such that, at first, laser beams are simultaneously irradiated onto equally spaced three points on the circumference, then the three irradiated positions are shifted on the circumference for simultaneous irradiation onto the new three points. In this way, as irradiated positions are shifted, the simultaneous irradiation onto three points is carried out two or three times. As a result, the radiation permits each joint portion secured by welding at the twelve to fifteen locations on the circumference. Each collimator is thus secured to the cylindrical member 112.
However, the laser welding technique causes the irradiated points to have different amount of contraction due to changes in laser""s radiated positions, irregularities of laser power, and/or differences in states of the welded locations. It is frequent that, as to at least one of the collimators 102, 104 and 110, the finally secured collimator angle results in an unexpected change from its optimum alignment angle that has been adjusted during its connection into the cylindrical member. Therefore, once such a situation occurs, the optical axes are mutually different between the input collimators 102 and 104 and the output collimator 110. This will lead to the problem that optical losses of the collimators in the secured state within the cylindrical member 112 are higher than expected.
It has therefore been long desired that an optical multiplexing module that causes no displacements in its optical axes, which might occur when at least two after-alignment optical parts are secured to a cylindrical member with welding, and a method of correcting such optical axes.
A first embodiment of the invention is an optical multiplexing module comprising:
(a) a cylindrical member (12) which is provided with an intermediate cavity (35), an optical multiplexing element (34), a prism (32) for changing an optical path of incidence light, which are aligned along an optical axis in the cavity (35), a first cylindrical cavity (26, 28) formed at an input side of the cylindrical member (12), and a second cylindrical cavity (30) formed at an output side of the cylindrical member (12);
(b) an output collimator (18) inserted and fixed in the second cylindrical cavity (30); and
(c) one or more input collimators (14, 16) inserted and fixed in the first cylindrical cavity (26, 28), an optical axis of the input collimators toward the output collimator (18) being adjustable by an optical axis adjusting means.
A second embodiment of the present invention is the optical multiplexing module, wherein the optical axis adjusting means for the input collimators comprises
(a) a ring (38) having a first end surface (38b) welded to an end surface of the cylindrical member (12) and a second end surface (38a) oppositely positioned to the first end surface, each of the first and second end surfaces forming a spherical surface, and
(b) a flange (42) being formed at an intermediate part of a cylinder of the collimator and having a tip (40) formed as a flat surface, the flange being line-contacted to the spherical surface (38a) and being welded to the ring.
A third embodiment of the present invention is the optical multiplexing module, wherein the welding is laser welding.
A fourth embodiment of the present invention is the optical multiplexing module, wherein the laser welding is either one of YAG laser welding and excimer laser welding.
A fifth embodiment of the present invention is the optical multiplexing module, wherein the welding is carried out so that an intensity of input light to the module and an intensity of output light from the module are measured and a loss between the measured intensity is minimized.
A sixth embodiment of the present invention is the optical multiplexing module, wherein, after the welding, the strength of input light to the module and the intensity of output light from the module are measured again, and the welding is carried out so that the loss between the measured intensity are minimized.
A seventh embodiment of the present invention is a method of adjusting an optical axis of an optical multiplexing module, comprising the steps of:
(a) preparing a cylindrical member (12) which is provided with an intermediate cavity (35), an optical multiplexing element (34) and a prism (32) for changing an optical path of incidence light which are contained along an optical axis in the cavity (35), a first cylindrical cavity (26, 28) formed at an input side of the cylindrical member (12), and a second cylindrical cavity (30) formed at an output side of the cylindrical member (12);
(b) inserting an output collimator (18) into a cylinder of the second cylindrical cavity (30), then securing the output collimator in the cylindrical member (12) by welding; and
(c) inserting one or more input collimators (14, 16) into the first cylindrical cavity (26, 28), then adjusting optical axes of the input collimators and the output collimator and fixing so that a measured optical loss between the input and output collimators is minimized.
An eighth embodiment of the present invention is the method of adjusting the optical axis of the optical multiplexing module, wherein the adjusting and fixing include
(a) spot-welding a ring (38) to an end surface of the cylindrical member (12), the ring having a first end surface (38b) and a second end surface oppositely positioned to the first end surface, each of the fist and second end surfaces being formed as a spherical surface (38a), and
(b) contacting a tip (40) of a flange (42) being formed at an intermediate part of a cylinder of the collimator with the spherical surface (38a) of the ring, then adjusting an angle of the flange (42) to the ring (38) and spot-welding the flange to the ring.
A ninth embodiment of the present invention is the method of adjusting the optical axis of the optical multiplexing module, wherein the fixing is carried out a plurality of times.
A tenth embodiment of the present invention is the method of adjusting the optical axis of the optical multiplexing module, wherein the fixing carried out at and after the second time comprising:
(a) monitoring an optical loss between the optical input-side collimators and the optical output-side collimator, and applying an external force in turn to a plurality of arbitrary positions along a peripheral of a connected part of one collimator to search a hit point showing a maximum reduction in the optical loss, and
(b) carrying out the spot welding at a position (80) of the collimator opposite to the hit point by 180 degrees.
An eleventh embodiment of the present invention is the method of adjusting the optical axis of the optical multiplexing module, wherein the spot welding is laser welding.
A twelfth embodiment of the present invention is the method of adjusting the optical axis of the optical multiplexing module, wherein the laser welding is either one of a YAG laser and an excimer laser.